CONICET | Buscador de Institutos y Recursos Humanos

Territorial aggression has been widely studied in males and it has been historically suggested that androgens arekey mediators of this behavior. However, more recent evidence suggests that it is the aromatization to estrogens,rather than androgens themselves, that is key to regulating this behavior. Females also display aggressive be-haviors, but the physiological regulation of female aggression is still understudied when compared to males. Inthis context, the challenge hypothesis postulates that male-male aggressive interactions stimulate the productionof androgens in males in periods of social instability. Here we determine plasma sex steroid levels in Cichlasomadimerus to assess whether estrogens are related to aggressive behavior and to test the challenge hypothesis inboth males and females. We set-up challenge trials as intrasexual dyadic encounters and determined androgenand estrogen levels before and after the trial in both winners and losers. Even though there were no di erences inﬀinitial estradiol-17 plasma levels between male winners and losers, initial levels were higher ( = .046) inβ p female winners than in losers, while there were no di erences in testosterone or 11-ketotestosterone levels. Afterﬀtrials, both males and females showed elevated levels of estradiol-17 and both androgens, but only malesβ exhibited a signi cant 1.45, 5.42 and 3.2-fold increase in estradiol-17 , testosterone and 11-ketotestosterone,ﬁβrespectively ( = .023, = .016, = .018). Moreover, changes in circulating levels of estradiol-17 in femalesp p p β after the trials do not depend on their reproductive status or on the outcome of the contest. We suggest thatfemale aggression is associated with initial levels of estradiol-17 , and that the challenge hypothesis, originallyβde ned for androgens, could also be extended to estrogens.